Jon, ANYONE who has hunted much has lost a perfect zero in the field, whether with iron or glass sights.
I just yesterday held off from shooting a deer at a measily 100 yards with a M-94 trapper .30-30 that I had with nearby, because I had just ascertained that the excelent iron Lyman sights on it had been knocked off so that it shoots 6" high and right at 50 yards! THIS would account for why my father missed a nice buck last year with it at about 75 yards! We frankly never even considered that those foolproof sights could be off.
Earlier in the day, my hunting buddy fired FOUR times at a deer before connecting and dropping the animal at 100 yds. The shots were just skimming over the top of the shoulder. Finally he lowered his aim, and dropped the animal with a spine shot. Turned out his rifle (never hunted before) had shifted its zero from 2.5" high at 100 to 5" high at 100. Rifle: Win M-70. Scope: Simmons 3X9. No noticable knocking...
It happens to the Best of us.